Li-ion batteries in portable electronic devices typically undergo different charging, discharging and storage routines based on their use. Batteries that employ Li-ion cell chemistry will produce gas when they are electrically overcharged beyond established safety limits. This gas may be used to trigger pressure activated safety devices to improve the reliability and safety of batteries. A current interrupt device (CID) is typically employed to provide protection against any excessive internal pressure increase in a battery by interrupting the current path from the battery when pressure inside the battery is greater than a predetermined value. The CID typically includes a rupture disc and a pressure disc in electrical communication with each other. The rupture disc and the pressure disc are, in turn, in electrical communication with an electrode and a terminal of the battery, respectively. The pressure disc separates from (e.g., deforms away or is detached from) the rupture disc of the CID when pressure inside the battery is greater than a predetermined value, whereby a current flow between the electrode and the terminal is interrupted.
Generally, however, CIDs known in the art activate at a relatively high pressure, for example, at an internal gauge pressure greater than about 15 kg/cm2. Typically, when any excessive internal pressure increase that triggers such CID activation occurs, the internal temperature of the battery is also relatively high, causing additional safety issues. High temperatures are a particular concern in relatively large cells, such as cells larger than “18650” cells (which have an outer diameter of about 18 mm and a length of 65 mm).
Further, CIDs typically are fabricated in conjunction with fabrication of the remainder of the battery and require a low tolerance for variation to ensure activation at an appropriate pressure. In some designs the surface area available for welding of a tab from the jelly roll of a battery typically is limited due to need to provide gas pressure conduits. The gas pressure conduits in the disc often includes at least one through-hole that must not be blocked during welding of tabs from the jellyroll to the rupture disc.
The surface area of the pressure disc is one of the factors that affect its actuation or reversal pressure, material thickness being another. In prismatic or non-circular cells, the shortest side of the cell typically dictates the maximum size of a circular pressure disc that can be used. Within the envelope of any given prismatic cell design, it is possible to achieve lower activation or reversal pressures by using an elongated pressure disc (oblong, oval, etc.) compared to a circular pressure disc of the same material thickness.
Therefore, there is a need for CIDs for batteries, particularly relatively large lithium-ion batteries, that can reduce or minimize the aforementioned problems.